This invention relates to compression bonding methods, and more particularly to methods for bonding optical elements such as glass optical fibers and glass lenses to aluminum.
Optical communication systems typically include a variety of optoelectronic devices (e.g., light sources, photodetectors, switches, modulators, amplifiers, and filters). For example, in the optical communication system 1 shown in FIG. 1, a light source 2 generates an optical signal. The optical signal comprises a series of light pulses. The light pulses are transmitted from the light source 2 to a detector 5. Typically, an optical fiber 4 transmits the light pulses from the light source 2 to the detector 5. The optical fiber 4 preferably has amplifiers (not shown) and filters (not shown) positioned along its length. The amplifiers and filters propagate the light pulses along the length of the optical fiber 4 from the light source 2 to the detector 5.
The light pulses propagated from the light source 2 to the detector 5 are typically coupled from the optical fiber 4 to the optoelectronic devices (or vice versa) with an optoelectronic module. A schematic view of an optoelectronic module 6 useful for coupling light pulses from an optical fiber to an optoelectronic device is shown in FIG. 2.
The optoelectronic module 6 includes a support 7, a lens 8, an optical fiber 9, and an optoelectronic device 10. The lens 8 couples the light between the optical fiber 9 and the optoelectronic device 10.
The lens 8 and the optical fiber 9 are typically made of glass. The support 7 is typically made of silicon. Silicon etches preferentially along predictable crystallographic planes, so grooves, cavities, and alignment indentations suitable for supporting the lens 8 and/or the optical fiber 9 are easily formed by masking and etching various surfaces of the silicon support. The lens 8, the optical fiber 9, and the optoelectronic device 10 are preferably bonded to the support 7. The optoelectronic device is typically soldered to the support. In one technique, the lens and/or the optical fiber is bonded to the support with an adhesive such as an epoxy. However, epoxies potentially provide a source of contamination for the optoelectronic module. For example, epoxies typically outgas solvents, which will not allow hermetic sealing of the optoelectronic package. Furthermore these solvents can be absorbed by the facet coating of the optoelectronic device leading to eventual failure of the coating and device.
Alternatively, the lens and/or optical fiber are bonded on the support using thermo-compression bonding, as shown in FIG. 3. In thermo-compression bonding, the grooves and cavities used to support the lens or the optical fiber are coated with a layer of aluminum 11. Thereafter, the lens and/or the optical fiber are bonded to the aluminum surfaces of the support by applying pressure 12 and heat 13 to the interface between the lens and/or the optical fiber and the aluminum layer. For example, a force greater than about 1000 grams applied for more than 30 seconds at a temperature between about 350xc2x0 C. to about 400xc2x0 C. is typically required to bond a glass lens to an aluminum coated silicon support.
Heating the support at temperatures between about 350xc2x0 C. to about 400xc2x0 C. for times greater than 30 seconds potentially affects the solder bonds used to bond the optoelectronic device to the support. For example, AuSn is typically used to bond optoelectronic devices to the silicon support. AuSn flows at a temperature of about 285-330xc2x0 C., so optoelectronic devices attached therewith potentially move as the solder attaching them reflows. Additionally, many lenses are coated with an antireflective (AR) coating. The AR coatings reduce reflections off of surfaces at a wavelength determined by the properties of the coating. Forces greater than about 1000 grams potentially fracture the AR coatings on the lenses, causing some bonds (about 5-10%) to have low bond strengths.
A method for bonding an oxide-containing member to an aluminum surface, comprising the steps of: providing a substrate, wherein a portion of a surface of the substrate has aluminum thereon; positioning an oxide-containing member on the aluminum surface of the substrate; and bonding the oxide-containing member to the aluminum surface by pressing the oxide-containing member against the aluminum surface while simultaneously heating the interface between the oxide-containing member and the aluminum surface, wherein the interface between the oxide-containing member and the aluminum surface is heated with a laser.
Desirably, the interface can be heated by a resistive heater to a temperature below the melting point of the solders of the assembly and localized heating via the laser light can be used to reach the final temperature for bonding without affecting the solder bonds already in place on the substrate.